1. Field of the Invention
The present invention relates to semiconductor storage devices, and more particularly to low cost memory resulting from manufacturing efficiencies which construct the devices in three-dimensions and which incorporate efficient testing mechanisms.
2. Description of Prior Art
Many versions of three-dimensional memory arrays have been disclosed in the prior art and they might be classified as being one of two types—stacked chips and layered manufacture.
Layered approaches are discussed in U.S. Pat. Nos. 4,525,921, 4,646,128, and 5,432,729 wherein Carson disclosed a technique for bonding two or more memory chips one on top another to form a three-dimensional memory array. There have been variations on this design, such as by Kato in U.S. Pat. No. 5,051,865, in which he discloses an enhancement comprising heat sink layers which are bonded between memory circuit layers to help reduce overheating.
Of greater interest to the present invention, Zhang, in his U.S. Pat. No. 5,835,396, discloses an approach for manufacturing a layered memory device based on diode storage devices at the intersections of the rows and columns within each layer and Rosner, in his U.S. Pat. No. 4,442,507, discloses an electrically programmable read-only memory. Both of these devices are manufactured upon a semiconductor substrate having decoding logic for the associated bit lines of the memory layers.
However, all of these devices have shortcomings. The bonding of multiple chips creates many points of failure and has high associated assembly costs. Manufacturing devices in layers as disclosed in the prior art has the high cost of the base substrate and its electronic circuitry (manufactured using traditional semiconductor manufacturing means) and its associated complexity as well as the many potential points of failure of interconnecting the vast number of row and column bit lines of the various layers.
What is needed is a three-dimensional memory device which can retain the advantage of lower cost manufacturing by not requiring a base layer comprising the bit line decoding circuitry and the high reliability of few layer interconnects. The present invention accomplishes this by including the decoding circuitry on each memory layer thereby eliminating the need for a base layer comprising bit line decoding circuitry and thereby dramatically reducing the number of layer interconnects to just power and a few address and data lines.